An essential feature of inflammation is the emigration of leukocytes from the blood into damaged or infected tissue. Several evidences suggest that extracellular nucleotides play a critical role in leukocyte emigration via activation of the P2Y2 subtype of nucleotide receptors (P2Y2R). Damaged cells as well as activated platelets, mast cells, macrophages, and nerve cells can release nucleotides into the extracellular environment where they activate many subtypes of nucleotide receptors. Activation of the P2Y2R subtype in monocytes, neutrophils, and other leukocytes has been shown to have a mitogenic and chemotactic effect on these cells. Furthermore, tissue damage or stress has been found to dramatically increase the expression of the P2Y2R in vascular endothelial cells and extravascular application of the P2Y2R agonist UTP to injured tissue enhances monocyte adhesion to endothelial cells and transendothelial migration of monocytes to the site of injury. We have found that the P2Y2R contains an integrin-binding domain that allows this receptor to associate with the aV[unreadable]3 integrin, an adhesion molecule that is important for both leukocyte migration and angiogenesis. Furthermore, integrin association with the P2Y2R has been found crucial for chemotaxis or cell migration towards extracellular nucleotides. The central hypothesis of this study is that leukocyte emigration caused by extracellular nucleotides is mediated by P2Y2Rs in both leukocytes and endothelial cells and is coordinately regulated by the association between P2Y2R and aV[unreadable]3 integrins. Our overall objective is to understand how tissue damage causes the body to mount an inflammatory response. Briefly, the studies in this proposal will 1) identify signaling molecules and protein complexes that are responsible for P2Y2R-mediated chemotaxis and 2) use the P2Y2R knockout mouse and an in vivo model of vascular injury to conclusively determine whether the P2Y2R is involved in recruitment of monocytes and other immune cells into damaged tissue. We suggest that a greater understanding of the mechanisms of P2Y2R function and regulation will lead to drug therapies that control inflammation. Nucleotides released from damaged tissue have been implicated as inducers of inflammation via activation of P2Y2 nucleotide receptors (P2Y2R) present on the surface of leukocytes and vascular endothelial cells. Therefore, the P2Y2R represents an exciting new target for controlling inflammation and our proposed research into the molecular biology of the P2Y2R should enable us to devise therapeutic procedures to stimulate or limit inflammatory responses mediated by this receptor.